WO1996037444A1

WO1996037444A1 - Method of aerobically treating wastewater and treatment tank

Info

Publication number: WO1996037444A1
Application number: PCT/JP1996/001365
Authority: WO
Inventors: Noboru Katsukura; Takehiko Yamada; Kouji Mishima; Akinori Nishii; Souta Nakagawa; Eiji Tochikubo
Original assignee: Ebara Corporation
Priority date: 1995-05-23
Filing date: 1996-05-23
Publication date: 1996-11-28
Also published as: EP0933334A4; DE69626864D1; US6077424A; CA2221923A1; KR19990021838A; EP0933334A1; CN1188462A; KR100409056B1; CN1098815C; EP0933334B1; DE69626864T2

Abstract

A method of treating wastewater with a microorganism immobilized on carriers and an aerobic treatment tank for use therein. One or more submerged agitation aerators provided with an air-diffusing mechanism on the delivery side of an impeller are disposed in the treatment tank to atomize a mixture of air and wastewater and circulate the carriers and wastewater in the treatment tank through the aerators, thus distributing the carriers nearly uniformly in a suspended state in the tank. The delivery port of the aerator is disposed so as to open in the vicinity of the bottom or the intermediate section of the tank. In the latter case, the aerator sucks up the carriers and wastewater from the vicinity of the tank bottom through a draft tube extending toward the bottom.

Description

Specification

Aerobic treatment method and treatment tank for sewage

(Technical field to which the invention belongs)

The present invention relates to an aerobic treatment method for sewage and a treatment tank therefor, and more particularly to a method for holding sewage, human waste, organic industrial wastewater, etc., by holding a microorganism-immobilized carrier in an aerobic treatment tank. The present invention relates to a biologically aerobic treatment method and a treatment tank therefor. (Conventional technology)

In recent years, activated sludge method, biofilm method, immobilized microorganisms method, etc. are known as sewage treatment technology, but from the viewpoint of efficient use of land, development of sewage treatment method with a smaller area is awaited. Aerobic treatment of sewage using a carrier on which microorganisms are immobilized is attracting attention, coupled with improved performance of the carrier material. The present inventors have also previously developed a sewage treatment apparatus shown in FIG. 9 using a carrier on which microorganisms are immobilized. In the treatment apparatus shown in FIG. 9, sewage is introduced from the inflow pipe 7 to one end of the treatment tank 1, aerated in the treatment tank 1, becomes treated water, and flows out through the outflow pipe 8. In the treatment tank 1, the carrier 2 on which the microorganisms are immobilized is maintained in a floating state by the fine bubbles supplied from the diffusing means 3 such as a diffuser and a diffuser tube.

The air diffuser 3 is disposed on the bottom of the treatment tank 1 and is supplied with pressurized air from the blower 4 via the air pipe 5, and supplies countless fine bubbles to the sewage from near the bottom of the treatment tank. The myriad of fine bubbles rise up in the sewage and partially dissolve in the sewage. The carrier 2 in the sewage is pushed by the rising fine bubbles and rises in the treatment tank 1, and sinks by its own weight in an area where the fine bubbles do not rise, circulates in the wastewater and is maintained in a floating state. A carrier separator 6 is arranged at the other end of the treatment tank 1 and separates the carrier from the treated water flowing out of the treatment tank.

In the prior art, as an aerator that diffuses and mixes air into sewage for sewage treatment, there are aerators that stir the surface of sewage and those that diffuse air through a number of small holes into sewage. Underwater agitation type aerators with air diffusers on the discharge side (airers with blades) are disclosed in, for example, Japanese Patent Publication No. 61-36475, Japanese Patent Publication No. 61-364746 And JP-B-61-380000, and U.S. Pat. No. 4,512,936. The treatment tank 1 in FIG. 9 has the advantages that the oxygen dissolving efficiency of the diffusing means 3 is high, the stirring power by the diffusing means 3 is small t, and thus the carrier 2 is not destroyed t. Had disadvantages.

(1) The carrier 2 on which microorganisms are immobilized flows in the horizontal direction from the inflow end of the treatment tank 1 (the left end of the treatment tank in Fig. 10) to the outflow end together with the water to be treated. Low near the inflow end of the treatment tank 1 and high near the outflow end, the treatment tank 1 becomes uneven and the treatment capacity of the treatment tank is low. Further, the carrier separator 6 was subjected to a force for preventing the flow of a large amount of the carrier, and a large amount of the carrier was gathered in the vicinity of the carrier separator 6, which hindered the separation of the carrier and the treated water.

(2) Carriers settle and accumulate between the vertical position of the air supply opening of the air diffuser 3 located on the bottom of the treatment tank 1 and the bottom of the treatment tank, and they do not circulate in the wastewater. Does not work.

For these reasons (1) and (2), it was necessary to supply a carrier that greatly exceeded the planned and expected carrier volume in order to generate the required treatment capacity in the treatment tank.

(3) The air diffuser 3 must be provided with an air supply pipe at the bottom of the tank, and it has a large area with many small holes and is easily clogged. It was necessary to replace the guard, but when replacing the air diffuser 3, it was necessary to remove a large amount of carrier outside the treatment tank.

(4) In order to solve the disadvantages of (1) and (3) above, it was considered to install a barrier to prevent the carrier from flowing in the horizontal direction and to install a stirring and transferring means. Had problems in terms of processing capacity, equipment costs, and operating costs (Japanese Unexamined Patent Publication No. 7-124,582, Japanese Unexamined Patent Publication No. Hei 7-136678, Japanese Unexamined Patent Publication No. No. 1,366,799, Japanese Patent Application Laid-Open No. Hei 7-136,680).

(5) In order to solve the disadvantage of the above (2), mortar is used to fill the area (dead zone) where the carrier does not circulate between the vertical position of the air supply opening of the air diffuser 3 and the bottom of the processing tank. The installation of a sedimentation prevention plate to prevent the sedimentation of the carrier in the dead zone was considered, but the construction was difficult and the cost was high.

Also, when the immobilized carrier is used in an aerobic treatment tank (deep aeration tank) having a large water depth, for example, a water depth of about 10 m, the carrier precipitates at the bottom and the treatment performance is remarkable. Dropped. Installing a diffuser at the bottom of the treatment tank to prevent carrier sedimentation has the disadvantage that a high-pressure blower is required to spray a fine air stream at a large water depth, which increases equipment costs. Furthermore, when a fine air stream was injected into the wastewater from a large water depth of about 1 Om, there was a problem that nitrogen gas was excessively dissolved in the wastewater and sludge floated up in the final sedimentation basin.

(Problems to be solved by the invention)

It is an object of the present invention to provide a method and a tank for aerobic treatment of sewage, which eliminates the disadvantages of the prior art. More specifically, an object of the present invention is to sufficiently stir and circulate the sewage and the microorganism-immobilized carrier (or activated sludge when coexisting with activated sludge) in the aerobic treatment tank and circulate the carrier (and activated sludge). ) Is to be evenly distributed in sewage. Another object of the present invention is to prevent carriers from accumulating on the bottom surface of the processing tank. Another object of the present invention is to make it possible to replace the air diffusing means without removing the carrier out of the treatment tank. Still another object of the present invention is to provide a deep aeration tank which prevents the bottom of the carrier from being settled in a treatment tank having a large depth, and also prevents a problem associated with dissolution of excessive nitrogen gas in sewage. It is. Still another object of the present invention is to provide an aerobic treatment method and a treatment tank which are energy-saving and have high oxygen dissolving efficiency. Other objects and advantages of the present invention will become apparent in the following description and accompanying drawings.

(Means for solving the problem)

In the aerobic treatment tank of the present invention, a method for treating sewage by using a carrier on which microorganisms are immobilized includes a submerged stirring type aeration device (submerged air cleaner) in which an aeration mechanism is arranged on the discharge side of an impeller. Placed and operated in the treatment tank, mix air into sewage and make it finer, and circulate carrier and sewage in the treatment tank through a submerged agitating aerator to distribute carrier almost uniformly in the treatment tank It is to let. In the method of the present invention, it is preferable to use a carrier in which microorganisms are immobilized and activated sludge together.

In the aerobic sewage treatment tank for aerating the sewage by holding the carrier in which the microorganisms are immobilized in the sewage and aerating the sewage, a submerged stirring type aeration apparatus equipped with an aeration mechanism on the discharge side of the impeller comprises: One or more units are placed in the tank. The underwater stirring type aeration device is configured so that the carrier and wastewater circulate through the treatment tank through it. By the operation of the apparatus, the carrier is substantially uniformly suspended and distributed in the sewage in the treatment tank. In the case of a treatment tank having a relatively shallow water depth, the underwater stirring type aeration apparatus preferably has a discharge port disposed near the bottom surface of the treatment tank and directed downward or laterally.

In the case of a deep aeration tank with a relatively deep water depth, the underwater stirring type aeration device is installed so that the discharge port opens upward in the middle water depth of the aeration tank. The term “intermediate water depth” as used herein refers to an arbitrary position between the water surface and the bottom of the tank. In practice, a distance of 5 m to 6 m from the water surface is the most efficient and preferable. In the case of a deep aeration tank, the underwater stirring type aeration device is equipped with a draft tube extending to the bottom of the deep aeration tank, and sucks the carrier and sewage from near the bottom of the aeration tank.

The present invention solves the disadvantage of the prior art that the carrier accumulates at the end of the aerobic treatment tank due to the flow inside the treatment tank, and is based on a general aeration method using fine bubbles supplied from a diffuser or a diffuser. Instead of a one-sided swirling flow system, a submerged stirring type aerator with excellent ability to form a stirring flow is provided. Underwater agitation type aerators are provided with an appropriate number of units at appropriate positions so that a uniform agitated flow is generated according to the shape of the processing tank, so that the suspended carriers continue to be uniformly dispersed in the tank. Such carrier bias is unlikely to occur.

In addition, unlike the diffuser and the diffuser, there is no need to attach an air pipe to the bottom of the aeration device when cleaning the aeration tank. Just lift and lower.

The aerobic sewage treatment tank and the deep aeration tank of the present invention can be incorporated into a treatment device for denitrifying sewage or a treatment device for denitrifying and dephosphorizing sewage. When sewage is subjected to anaerobic treatment and aerobic treatment, it is preferable to return the carrier to the aerobic treatment tank and return the sewage to the anaerobic treatment tank. When the liquid is separated and returned in this way, the pump capacity increases. Further, as a transfer pump provided at the outflow end of the aerobic treatment tank, an air lift pump, a non-blocking vortex pump, or a single screw pump can be used so that the carrier or the biofilm is not destroyed. It is desirable that the amount of water transferred can be arbitrarily changed, for example, by changing the motor speed by frequency control.

In transporting the carrier and sewage, other than pumps, means capable of transporting the carrier and biofilm without destruction may be appropriately used. Furthermore, Japanese Patent Application Laid-Open No. Hei 5-2-2613 Even if a carrier separating means such as a hydrocyclone or a trommel sieve is provided in the middle of the carrier transfer pipe as in the disclosed device, water is distributed to each treatment device provided in the preceding stage, and the carrier is distributed to the aerobic treatment tank. Good. The aerobic treatment method and the treatment tank of the present invention include, for example, sequentially connecting an oxygen-free process, an aerobic process, and a sedimentation process, circulating the effluent of the aerobic process to the anoxic process, A circulating nitrification denitrification method and apparatus for returning sludge to the anoxic process, or an anaerobic process is provided before the anoxic process, and the settled sludge from the settling process is returned to the anaerobic process, and denitrification It can be used in the aerobic treatment step and the aerobic treatment tank in the dephosphorization activated sludge method.

In the present invention, one or more underwater stirring type aerators are installed in the aerobic treatment tank. If the vertical cross section of the processing tank is rectangular in the vertical direction, install multiple underwater stirring aerators so that the flow in the tank does not shift, stir the inside of the processing tank evenly, and change to a submerged stirring aerator. By maintaining the aerobic condition in the treatment tank uniformly by the air supply, maintenance and periodic inspection work can be greatly reduced. The microorganism-immobilized carrier usable in the present invention is preferably a particulate carrier composed of sand, activated carbon, polyurethane foam, polyvinyl alcohol, polypropylene, polyethylene, polyethylene glycol, cellulose, etc., but is not necessarily limited to these carriers. . The apparent specific gravity of the carrier is preferably a little heavier than the sewage of the liquid to be treated, for example, about 1.02. As a method for immobilizing microorganisms on a carrier, an adhesion immobilization method is generally used, but an inclusive immobilization method is also applicable. Preferably, at the outflow end of the aerobic treatment tank, a carrier outflow prevention means such as a net, a grating, a punching plate, or an edge wire screen for preventing the outflow of the carrier is provided.

In another embodiment of the present invention, in a deep aeration tank using a fluid bioimmobilized carrier, an upper discharge type submerged mechanical stirring type aeration apparatus having a discharge port in a deep part of the intermediate water of the aeration tank is arranged. Then, the suction part of the aeration apparatus and the tank bottom are connected by a draft tube. In the deep aeration tank, a plurality of aeration devices are installed, and they are arranged in a single row or multiple rows in the longitudinal direction of the aeration tank.The aeration tank is designed such that the bottom of the tank faces the suction port of the draft tube, It can be tilted for easy movement.

(Action)

According to the present invention, a submerged stirring type aeration apparatus having an excellent stirring function is used.

-0- By uniformly stirring the inside of the aerobic treatment tank without adding an extra carrier that does not perform its function while being deposited at the bottom of the aerobic treatment tank, the carrier can be greatly improved in bias. In addition, according to the present invention, the use of a submerged stirring type aerator in the aerobic treatment tank reduces the oxygen dissolving efficiency due to the secular change due to clogging of the aeration means as compared with the conventional full aeration method using fine bubbles. Therefore, high processing performance can be obtained in an aerobic processing tank. Furthermore, it is not necessary to remove the carrier during maintenance of the aeration apparatus.

(Brief description of drawings)

FIG. 1 is a plan view showing a first embodiment of the aerobic treatment tank of the present invention.

FIG. 2 is a vertical longitudinal sectional view of the processing tank of FIG.

FIG. 3 is a schematic vertical sectional view of a nitrification denitrification apparatus incorporating the aerobic treatment tank of the present invention.

FIG. 4 is a configuration diagram showing a deep aeration tank according to a second embodiment of the present invention. FIG. 4a is a plan view, FIG. 4b is a cross-sectional view taken along line AA of FIG. 4a, and FIG. 4B is a sectional view taken along line BB of FIG. 4A.

FIG. 5 is a configuration diagram showing a deep aeration tank according to a third embodiment of the present invention. FIG. 5A is a plan view, FIG. 5B is a sectional view taken along line AA of FIG. 5A, and FIG. Is a cross-sectional view taken along the line BB in FIG. 5A.

Figure 6 is a schematic vertical cross-sectional view of a nitrification denitrification system incorporating a deep aeration tank.

FIG. 7 is a schematic vertical sectional view of the first embodiment of the underwater stirring type aeration apparatus used in the present invention.

FIG. 8 is a schematic vertical sectional view of a second embodiment of the underwater stirring type aeration apparatus used in the present invention.

FIG. 9 is a schematic vertical sectional view showing a conventional aerobic treatment tank using a carrier. (Best mode for carrying out the invention)

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to these embodiments, but is defined by claims. In the accompanying drawings, the same members and the like are denoted by the same reference numerals, and redundant description will be omitted. Figure

1 is a plan view showing an embodiment of an aerobic treatment tank of the present invention, and FIG. It is a longitudinal section of a tank. One underwater stirring type aeration device 30 is arranged in each of the first half and the second half of the plane of the processing tank 1 which is bisected by the broken line 16 in FIG. The broken line 16 is for explaining the position, and does not mean that a partition plate is provided in the processing tank 1 or the like. The vertical and horizontal dimensions of each half of the plane of the processing tank 1 are preferably 1: 1. As shown in FIG. 2, a circulating flow F is formed in the processing tank 1, and the microorganism-immobilized carrier 2 is substantially uniform throughout the processing tank 1 by such a circulating flow F regardless of the presence of the partition plate. Disperses and floats.

A carrier transfer pump 10 can be installed at the outflow end of the treatment tank 1 to prevent the concentration of the carrier at the outflow end due to the flow of the water to be treated (sewage) in the treatment tank 1. The carrier transfer pump 10 sucks the carrier 2 near the outflow end and transfers it to the inflow end via the conduit 11. The provision of the carrier pump enables fine adjustment of the carrier concentration in the processing tank 1. 1 and 2 is equipped with a carrier separator 6, a treated water outflow pipe 8, a blower 4, an air pipe 5, an air flow meter 9, and the like. The treatment tanks shown in Fig. 1 and Fig. 2 are equipped with a submersible aeration type aeration device instead of the conventional air diffuser that supplies fine air bubbles, to achieve stable oxygen dissolution efficiency despite aging. Obtainable. As a result, high processing performance can be obtained, and maintenance and inspection work can be significantly reduced.

FIG. 3 is a schematic vertical cross-sectional view of a nitrification denitrification treatment apparatus incorporating an aerobic treatment tank. In FIG. 3, the aerobic treatment tank 1 has the same configuration as the aerobic treatment tank 1 in FIG. 2, and is used in combination with the oxygen-free tank 12. In the nitrification denitrification treatment apparatus shown in Fig. 3, sewage flows from the inflow pipe 7 to the oxygen-free tank 12 together with the nitrification circulating fluid after being separated into the carrier and the nitrifying circulating fluid by the separator 13 and denitrated. After being subjected to the nitrogen treatment, it flows into the aerobic treatment tank 1 from the inlet provided at the upper part of the wall 15 separating the anoxic tank and the aerobic treatment tank 1. In the treatment tank 1, a circulating flow is generated by a submerged stirring type aeration apparatus, and the sewage undergoes a sufficient nitrification treatment. The sewage treated in the treatment tank 1 flows out of the treatment tank 1 through the carrier separator 6. The carrier plus nitrifying circulating fluid transferred by the carrier transfer pump 10 is separated into the carrier 2 and the nitrifying circulating fluid 14 by the separator 13, and the nitrifying circulating fluid 14 is circulated to the oxygen-free tank 12. .

Next, an example of nitrification and denitrification using a nitrification and denitrification treatment apparatus incorporating the aerobic treatment tank 1 of FIG. 3 will be described. (a) Treated water: Urban sewage

(b) Device configuration

Oxygen-free tank: 4 Q Om ³ (residence time 4.0 hours)

Aerobic treatment tank: 400m ³ (residence time 4.0 hours)

"A total of 800m ³ (HRT = 8. 0 hours)

Of treated water: 100m ³ / h

Return sludge amount δθιη ³ , hour

Nitrification liquid circulation: 20 Om ³ / hour

ML S S: 200 Omg / Little

Aeration volume: Treatment tank A part; 300 Nm ³ , hour

Treatment tank B part; 30 ONm ³

In both treatment tanks A and B, one agitated underwater aerator with an oxygen dissolution efficiency of 15% is installed. In the treatment tank, it was confirmed that a circulating flow was formed by the underwater stirring type aeration device, and that the mixture was mixed uniformly. As a result of the detailed investigation, the deviation of the carrier in the treatment tank was within ± 5%. In addition, the nitrification performance could be kept high in the entire treatment tanks A and B, and the ammonia nitrogen in the treated water was always less than 1 mg / liter.

Next, a third embodiment of the present invention will be described with reference to FIG. Installation depth of H ₂ water stirred aerator 3 0, the discharge pressure of the blower, considering the supersaturation of the nitrogen gas 3 to 6 m are suitable, preferably, 5 m before and after. The draft tube 35 extending between the aeration device 30 and the bottom surface of the aeration tank 50 generally has a diameter of 40 mm to 240 mm, and has a diameter capable of securing a liquid rising flow rate at which the carrier 2 can stably rise. The carrier 2 is a granular hydrophilic gel having a particle size of lmm to 10 mm, a plastic piece, a polymer carrier having fibers entangled in a marimo shape, a sponge, a foamable ceramic, or the like.

The deep aeration tank 50 can be used as an air tank in the standard activated sludge method, a nitrification tank (aerobic tank) in the nitrification denitrification method, or an aerobic tank in the anaerobic-anoxic-aerobic method. A known aerator 30 can be used, but if the carrier is soft, the propeller installation position, rotation speed, Alternatively, it is necessary to take measures to prevent destruction, such as finishing the flow path smoothly. The deep aeration tank 50 in FIG. 4 has a width of 8 mx a length of 24 mx water depth (H ^ 1 Om) and has a raw water inflow section 32 and a treated water outflow section 38. in order to prevent the separator (carrier separation screen) 6 is provided. underwater agitation type aeration apparatus 30, those 15 kW installed three in the longitudinal direction of the aeration tank 50, installed water depth H ₂ is 5 The aeration device 30 is a top discharge type, and the suction part at the bottom of the aeration device and the tank bottom 39 are connected by a draft tube 35 having an inner diameter of 136 Omm. It is a hydrophilic gel with a specific gravity of 1.02, and its usage is 15 VZV% by volume.

Inside the aeration device 30, the stirring blade that excites the circulating flow rotates, and near the blade, air is ventilated from the air pipe 5 at a rate of 8 to 18 Nm ³ / hour. As a result, a flow pattern as shown by an arrow F in FIG. 1B is formed in the aeration tank, and the carrier 2 flows smoothly in the aeration tank without settling on the bottom surface 39. The liquid ascending flow velocity in the draft tube 35 at this time is 30 m to 4 OmZ. Since the sedimentation velocity of the carrier 2 is 2 m to 3 m / min, the carrier 2 stably rises in the draft tube 35.

FIG. 5 is a configuration diagram showing a deep aeration tank 50 according to the third embodiment of the present invention. FIG. 5A is a plan view, FIG. 5B is a cross-sectional view taken along line AA of FIG. 5A, and FIG. 5B is a sectional view taken along line BB of FIG. 5A. FIG deep aeration tank 50 of 5 is the width 8mx length 20mx water depth (H ^) 10m, 2 units over 5 kW discharge type underwater agitation type aeration apparatus 30 7., which was placed in a water depth (H ₂₎ 5 m It is. In this example, the carrier 2 was settled at the corner of the aeration tank 50, so a 30-degree inclined surface 37 was provided on the bottom of the tank toward the suction port of the draft tube 35.

Using a specific gravity-adjusted plastic piece having a particle size of 5 mm and a specific gravity of 1.03 as a carrier 2 at 20% in the deep aeration tank 50 of FIG. 5, air was ventilated for 4 to 6 Nm ³ minutes. As a result, the flow pattern shown in FIG. 2B was formed, and the carrier 2 flowed smoothly in the aeration tank. In this embodiment, it is possible to make the carrier flow stably in the deep aeration tank. The underwater stirring type aeration device 30 can reduce the aeration power as compared with the swirling flow type. The underwater stirring type aeration device 30 must have strong stirring and mixing power in the tank. Therefore, the tank can be maintained in a completely mixed state. As a result, the carrier concentration in the tank can be made uniform, and the ability of the carrier can be maximized.

FIG. 6 is a schematic vertical cross-sectional view of a nitrification denitrification device incorporating a deep aeration tank. In FIG. 6, a deep aeration tank 50 was adopted as a nitrification tank (aerobic tank) 42 of a circulating nitrification denitrification device, and operated as follows.

(a) Raw water (introduced from raw water inlet 32):

Primary municipal sewage water: B 0 D 100 mg liter,

NH ₄ — N3 Omg / Little,

Water volume: 15.00 Om ³ /

(b) Deep aeration tank:

Denitrification tank 41: width 6.5mx length 31mx water depth 10m,

Effective volume: 2. 000m ^3.

Underwater stirrer 43: DSR-240UP

(Ebara Corporation, 30kW) x2 units,

Nitrification tank 42: width 6.5mx length 23mx water depth 10m,

Effective volume: 1. 470m ³

Underwater stirring type aerator 30: DSR-140UP (EBARA, 1 kw) x 3 units,

Draft tube: caliber 14 Omm X 4m X 3,

Aeration volume: 12 NmV (min · unit) X 3 units

(c) Carrier 2:

Material: hydrophilic gel made of polyethylene glycol,

Particle size: 4mm,

Specific gravity: 1.02,

.Input amount: 22 Om ³ as bulk volume (15VZV%)

(d) MLSS: 2500mg / liter

(e) Operation results:

A flow pattern as shown by arrow F in Fig. 6 was formed in the aeration tank, and the carrier flowed in the tank at a uniform concentration (15%) without settling on the bottom surface. As a result, The average water quality of the water (outflow from treated water outlet 38) is BOD 5.4 mg / litre, T—N 9 .S mg Z litre, NH ₄ —N 0.4 mg Z litre. Yes, very good.

FIG. 7 is a schematic vertical sectional view ′ of the first embodiment of the underwater stirring type aeration apparatus used in the present invention. The aeration device 60 in FIG. 7 is of a lower discharge type, and an impeller 59 provided with a blade 58 rotated by a motor 56 via a gear reducer 57 is housed in the outer casing 52. . The aeration device 60 sucks sewage and carrier from the suction port 51 opening upward, flows through the flow path 55 by the rotating blades 58, and the discharge port 62 opens laterally below. Discharge. The air casing 54 provided on the discharge side of the impeller 59 is supplied with pressurized air from the air pipe 5 and passes through the air discharge port 53 into the sewage flowing in the flow path 55 to form fine air. Supply air bubbles.

The distance between the outer casing 52 and the tip of the blade 58 is made larger than the diameter of the carrier, and the blade 58 is finished with a grinder in order to prevent the carrier from being destroyed by the aeration device 60 and the separation of microorganisms. The peripheral speed of the tip of the blade 58 is set to about 1 OmZ second or less.

FIG. 8 is a schematic vertical sectional view of a second embodiment of the underwater stirring type aeration apparatus used in the present invention. The aeration device 70 in FIG. 8 is of a top discharge type, and an impeller 59 having a blade 58 rotated by a motor 56 via a gear reducer 57 is housed in the outer casing 52. . The aeration device 70 sucks sewage and carrier from the suction port 71 opening downward, passes through the flow path 55 by the rotating blades 58, and the discharge port 開口 2 opening laterally upward. Discharge. An air casing 74 arranged at a part of the outer casing 52 on the discharge side of the impeller 59 is supplied with pressurized air from the air pipe 5, and flows through the air discharge port 53 through the flow path 55. Supply fine air bubbles into flowing treated water. The same measures as in the aeration apparatus 60 in FIG. 7 are taken to prevent the carrier from being destroyed by the aeration apparatus 70 and the microorganisms from being peeled off.

(The invention's effect)

According to the present invention, since the sewage and the microorganism-immobilized carrier in the aerobic treatment tank are subjected to a strong stirring action by the underwater stirring type aeration apparatus, the carrier is substantially uniformly distributed in the treatment tank in a floating distribution. Therefore, the sewage treatment capacity is improved, and the carrier is treated with the carrier in the carrier separator. The occurrence of a separation failure with water is prevented. In addition, strong agitation prevents the carrier from settling and accumulating between the vertical position of the air supply opening of the air diffuser arranged at the bottom of the processing tank and the bottom of the processing tank. Since the part can be fluidized and effectively used, the amount of carrier used can be reduced to the minimum necessary.

In addition, the underwater stirring type aerator equipped with an aeration mechanism on the discharge side of the impeller used in the present invention has a relatively small surface area and does not have many small holes. There is no need to remove it outside the processing tank. According to the aerobic treatment tank of the present invention, since prevention walls and agitation transfer means are not required, costs such as equipment costs and operation costs can be reduced. In addition, a region in which the carrier does not circulate is not generated in the processing tank, and high processing performance can be obtained in the entire processing tank.

According to another aspect of the present invention, in a deep aeration tank using a microorganism-immobilized carrier, by using a submerged stirring type aerator with a draft tube connected to a lower portion, bottom sedimentation of the immobilized carrier can be prevented. Furthermore, since the amount of aerated air can be reduced, energy-saving treatment can be performed, and the concentration of the carrier in the tank can be equalized, so that the capacity of the carrier can be maximized.

Claims

The scope of the claims

1. In a method of treating sewage by holding a carrier in which microorganisms are immobilized in a floating state in an aerobic treatment tank,

An underwater agitation type aeration device with an aeration mechanism on the discharge side of the impeller is arranged in the treatment tank and activated, and the air is mixed into the sewage to make it finer. The method is characterized in that the carrier is circulated in the treatment tank and the carrier is suspended and distributed almost uniformly in the treatment tank.

2. The method according to claim 1, wherein activated sludge is used in addition to the carrier on which the microorganisms are immobilized.

3. In an aerobic sewage treatment tank where the microorganism-immobilized carrier is kept suspended and the sewage is aerated.

One or more underwater stirring type aerators equipped with a diffuser mechanism on the discharge side of the impeller arranged in a casing having an inlet and an outlet are arranged in the treatment tank. The carrier and sewage are circulated in the treatment tank via the sewage treatment tank, and the carrier is substantially uniformly suspended and distributed in the treatment tank by operating the underwater stirring type aerator. .

4. The sewage treatment tank according to claim 3, wherein the underwater stirring type aeration apparatus has a discharge port near a bottom surface of the treatment tank.

5. The discharge port of the underwater stirring type aeration device is installed so as to open to the middle depth of the treatment tank. The underwater stirring type aeration device is a draft tube that extends from the underwater stirring type aeration device to the bottom of the treatment tank. 4. The sewage treatment tank according to claim 3, wherein the carrier and the sewage are sucked from near the bottom surface of the treatment tank through the fin.

6. The sewage treatment tank according to any one of claims 3 to 5, wherein the sewage treatment tank is incorporated in a treatment device for denitrifying sewage or a treatment device for denitrifying and dephosphorizing sewage.